The present invention relates to an anti-fogging and stain-prevented glass article, and in particular relates to an anti-fogging and stain-prevented sheet glass for buildings, and an anti-fogging and stain-prevented glass article used for glasses, mirrors, lenses, showcases, etc.
There has been a strong need for anti-fogging and stain-prevented glass plate mainly in the fields of automobiles and buildings since ever. In particular, as regards automobiles, it becomes an important theme to give anti-fogging and stain preventing properties to window glass in view of safe driving.
Conventionally, various kinds of anti-fogging and stain preventing coatings have been studied with respect to glass articles. For example, there are organic or inorganic thin film coating containing a surface-active agent (Japanese Laid-open Patent Publication No. 117202 of 1995, Method 1), hydrophilic polymer coating (Japanese Patent Publication No. 1344292, Method 2) and organic/inorganic composite film coating containing a hydrophilic organic functional group (Japanese Laid-Open Patent Publication No. 220428-1994, Method 3), etc.
Recently, anti-fogging and stain-prevented glass having a titanium oxide thin film, which acts as an photocatalytic film, coated on its surface has been proposed (For example, xe2x80x9cCeramicsxe2x80x9d 31, 837-840 (1996), published by Japan Ceramics Association Inc., Method 4). This utilizes that titanium oxide on the surface of glass absorbs ultra violet light, and the absorbed ultra violet light energy efficiently oxidizes and decomposes organic articles adsorbed on the glass surface, thereby causing a clean surface having a remarkably hydrophilicity to be obtained.
Furthermore, the anti-fogging and stain-prevented glass having the abovementioned titanium oxide thin film coated on its glass surface is composed of inorganic substances and is excellent in the mechanism strength, wherein as far as light is given thereto once stains are adhered thereto, the surface can be purified again to cause a hydrophilic surface to be restored. If the surface sustains hydrophilicity, city type lipophilic black stains are hardly adhered, and furthermore if adhered stains are easily eliminated by precipitation of rain (For example, xe2x80x9cPainting Techniquexe2x80x9d published by Riko Publishing Co., Ltd., January, 1995, 94-99(1995), xe2x80x9cNovel stain fogging type paintxe2x80x9d prepared by Toshiki Komatsusawa and Toshikazu Nakaiye; xe2x80x9cPainting Techniquexe2x80x9d 1996, October Special Issue, 95-102 (1995), xe2x80x9cContamination deterioration and Contamination-resisting painting techniquexe2x80x9d (Industrial Paint) prepared by Shoichi Tanaka). That is, the surface sustaining hydrophilicity has a self-cleaning property and such glass materials can be used as a stain preventing material.
Although the abovementioned method 1 is excellent in the initial performance, there is such a problem where the service life is short since the surface-active agent is gradually consumed. Furthermore, the abovementioned method 2 can not be applicable to glass for which a comparatively mechanical strength is required for automobiles and buildings although the same is an effective means in some cases. Furthermore, although method 3 is devised in order to meet the anti-fogging property and mechanical strength at the same time, the same has a limitation in both aspects. Still furthermore, in a case where stains are once adhered, there is such a problem where the anti-fogging property is remarkably lowered. Furthermore, although method 4 has in principle some features which can not be achieved by the other methods, with this method, anti-fogging and stain-prevented glass articles which can be used in practical aspects can not be achieved yet since the intensity of ultraviolet light in automobiles and buildings is very weak.
It is therefore an object of the invention to provide an anti-fogging and stain-prevented glass article, having excellent long-term anti-fogging and stain preventing properties, which can be used for window glass of automobiles and buildings, and for glasses.
The present invention provides an anti-fogging and stain-prevented glass article in which an alkali shut-off film and an photocatalytic film are laminated on the surface of glass substrate in the order, wherein the glass article has dents and projections, the arithmetical mean roughness (Ra) of which is 1.5 to 80 nm, and the mean interval (Sm) of which is 4 to 300 nm, formed on the photocatalytic film surface.
The invention provides an anti-fogging and stain-prevented glass article in which an alkali shut-off film, an photocatalytic film, and silicon oxide layer or an organic substance adhering preventing layer consisting of a layer of organosilane or its hydrolyzed substance having at least one functional group selected from groups consisting of polyalkylene oxide group, alkyl group, alkenyl group and aryl group in its molecule are laminated on its glass article in the order.
It is necessary to meet the three requirements at the same time in order to obtain excellent anti-fogging and stain preventing properties using an photocatalytic film; the first of which is to efficiently oxidize and decompose organic substances which will be cause of fogs and stains adsorbed on the surface of an photocatalytic film (that is, high photocatalytic activation), the second of which is that organic substances are hardly adsorbed on the surface (adsorption preventing property), and third of which is to reduce the apparent contact angle when water drops are adhered although necessary to secure an anti-fogging property (small contact angle). If the abovementioned three requirements are satisfied, it is possible to achieve excellent anti-fogging and stain preventing properties for a longer period of time.
In the invention, TiO2, ZnO, ZnS, WO3, Fe2O3, GaAs, CdSe, GaAsP, Cds, SrTiO3, GaP, In2O3 or MoO3, etc. may be used as a photocatalyst. TiO2 is photocatalyst which is most widely utilized at present in view of high photocatalytic activation and chemical stability, which can be favorably used in the invention. Hereinafter, a description is given of titanium oxide as a representative example.
Even though an photocatalytic film such as titanium oxide film is directly coated on the surface of glass substrate, high photocatalytic activation can not be obtained. This is because alkali metal ions such as Na ions, which come out from and are diffused from the glass substrate containing alkali metal in heat treatment, lowers the crystalization of the titanium oxide film. In order to prevent the crystalization of the titanium oxide film from being lowered, in the invention, a silicon oxide film or other alkali shut-off film is provided on the glass subtrate, and an photocatalytic film consisting of titanium oxide or an photocatalytic film containing titanium oxide is coated thereon. In a case where a film containing titanium oxide as an photocatalytic film is used, it is preferable that the content of titanium oxide is 10 or more percent by weight. If the content of titanium oxide is less than 10 percent by weight, the photocatalytic activation on the surface is lowered too much and this is not practical.
An anti-fogging and stain-prevented glass according to the invention has excellent anti-fogging and stain preventing properties and their sustainability and is excellent in mechanical strength, the same can be favorably used for automobiles, buildings and glasses.
Hereinafter, a description is given of the respective components of the invention.
[Alkali shut-off film]
As the abovementioned alkali shut-off film, a monocomponent or multicomponent composition selected from a group of silica oxide, aluminium oxide, titanium oxide, zirconium oxide and cerium oxide may be preferably used. Of them, a monocomponent of silica oxide or a multicomponent having silica oxide as its main component is preferable, and a two-component metal oxide consisting of silica oxide and zirconium oxide is further preferable. Since a metal oxide having silica oxide as its main component has a low refractive index and does not greatly spoil the photocatalytic characteristics of glass plate, it is preferable in view of formation of film. As regards a two-component metal oxide consisting of silica oxide and zirconium oxide, since its alkali shut-off property is very high, the same is further preferable, wherein a two-component metal oxide having the content of zirconium oxide at a ratio from 1 or more percent by weight to 30 or less percent by weight is most preferable. If the content of zirconium oxide is less than 1 percent by weight, there is no difference in the effect of improvement of the alkali shut-off property between zirconium oxide and monocomponent silica oxide. If the content thereof is 30 or more percent by weight, no more effect of improvement of the alkali shut-off property can be expected, and the reflection ratio is likely to be increased due to an increase of the refractive index. In this case, it becomes difficult to control the photocatalytic characteristics of glass plate, and this is not preferable.
It is preferable that the thickness of the abovementioned alkali shut-off film is from 10 nm or more to 300 nm or less. If the thickness if less than 10 nm, the alkali shut-off effect is not sufficient., and if the thickness is more than 300 nm, the interference color can be recognized to be remarkable, wherein it will become difficult to control the photocatalytic characteristics, and this is not preferable.
The abovementioned alkali shut-off film can be formed by an already-known method. For example, there are a sol-gel method (for example, Ceramics Association Journal, 90, P. 328 to 333 (1982) prepared by Yuji Yamamoto, Kanichi Kamiya, and Sumio Tsukuribana), a liquid-phase deposition method (for example, Japanese Patent Publication No. 59210/1989, and Japanese Patent Publication No. 13301/1992), a vacuum film formation method (vacuum evaporation, spattering), a baking method or spray coat (for example, Japanese Laid-open Patent Publication Nos. 124523/1978 and 96749/1981), a CVD method (for example, Japanese Laid-open Patent Publication Nos. 90441/1980, 201046/1989, and 208849/1993), etc.
[Photocatalytic film]
The photocatalytic activation of an photocatalytic film coated on the abovementioned alkali shut-off film greatly depends on the film thickness. If the film thickness is too thin, the optical catalyst film does not sufficiently absorb light, and if it is too thick, photocatalytic carriers produced in the film can not be sufficiently diffused outside the film. In either case, the catalyst activation is lowered. Although the most adequate film thickness differ according to the use condition, it is preferable that the film thickness is in a range from 10 nm to 500 nm, more preferably from 40 to 200 nm, in which a good photocatalytic activation can be achieved.
Although an photocatalytic film consisting of titanium oxide or an photocatalytic film containing titanium oxide of the invention is produced by using a usual film formation method, the sol-gel method is most preferably used. Sol can be obtained by hydrolyzing titanium alkoxide or titanium alkoxide along with other metal alkoxide at the same time. It is simple that a liquid available on the market, in which titanium oxide fine particles are dispersed in an inorganic binder (containing other metal alkoxide than titanium), and this is preferable used. As one of the examples of liquids which are available on the market, xe2x80x9cST-K03xe2x80x9d produced by Ishihara Industries Co., Ltd., and containing titanium oxide at a ratio of 5 percent by weight and inorganic binder at a ratio of 5 percent by weight), xe2x80x9cCA-62xe2x80x9d produced by Taki Chemical Co., Ltd, and containing titanium oxide at a ratio of 6 percent by weight and inorganic binder at a ratio of 1.5 percent by weight), etc. may be listed.
After a titanium oxide based thin film is formed on the alkali shut-off film, it is preferable that heat treatment is carried out at 450 to 650xc2x0 C. for ten minutes to two hours in order to improve the densification and crystalization of titanium oxide.
[Fluorine dope onto the photocatalytic film]
By doping a bit of fluorine atoms in the abovementioned photocatalytic film, there is a possibility that the photocatalytic activation is increased. Trifluoroacetate, etc. may be used as a dopant. A dopant such as trifluoroacetate, etc. is decomposed by subsequent heat treatment, and is doped into titanium oxide crystal grating as fluorine in a state of atom. Since the size of fluorine atoms is almost the same as that of oxygen atoms, it is considered that the doped fluorine atoms mainly exist in a form in which they are displaced by oxygen atoms of titanium oxide.
In a case where a titanium oxide based photocatalytic film is formed by a sol-gel method, fluorine atoms are doped into the film at a ratio of 0.002 to 1 percent by weight after the heat treatment such as burning is completed by adding a thermally decomposable fluorine compound such as trifluoroacetate (TFA) to a solution of titania-alkoxide which is the material thereof, or to a liquid in which titanium oxide fine particles are dispersed, and it is possible to increase the photocatalytic film activation.
Furthermore, in a case where a titanium oxide photocatalytic film is formed by a vacuum evaporation method or a chemical gas-phase deposition (CVD) method, it is possible to dope fluorine atoms by adding a fluorine compound to the material as in the above description.
If the amount of dope of fluorine atoms in the film is less than 0.002 percent by weight, the effect of increase of photocatalytic activation is not remarkable, and if the amount is more than 1 percent by weight, the photocatalytic activation is no more expected.
On the other hand, even by doping fluorine atoms into an alkali shut-off film, the fluorine atoms are diffused in a titanium oxide based film by heat treatment, wherein similar effects can be obtained. It is preferable that the amount of dope of fluorine atoms in the alkali shut-off film is from 0.002 or more percent by weight to 10 or less percent by weight. If the amount of dope of fluorine atoms in the alkali shut-off film is less than 0.002 percent by weight, an increase of the effect of photocatalytic activation of the photocatalytic layer is not remarkable, and if the amount thereof is more than 10 percent by weight, no more increase of the effect of the photocatalytic activation of the photocatalytic layer can be expected.
Doping of fluorine atoms into an alkali shut-off film is usually carried out by a method of adding a fluorine compound into the material thereof when forming an alkali shut-off film by a sol-gel method, a vacuum evaporation method, a baking method, a spray coat method, a CVD method, etc. Furthermore, in a case where an alkali shut-off film of silica is formed by a liquid-phase deposition method, since fluorine is included in the material solution (silica super saturation solution of silicofluoride hydroxide) at a ratio of 0.1 to 10 percent, it is not necessary to specially add fluorine to the material solution, the material solution can be used as it is.
[Dents and projections on the photocatalytic film surface]
In the present invention, dents and projections having an arithmetical mean roughness (Ra) from 1.5 to 80 nm and mean interval (Sm) from 4 to 300 nm therebetween are formed on the surface of an photocatalytic film which is coated on the abovementioned alkali shut-off film. Thereby, the contact angle with respect to water is made smaller, and more excellent anti-fogging property and long-term sustainability can be obtained.
In a case where the abovementioned Ra value is less than 1.5 nm or more than 80 nm, the long-term stability of the anti-fogging performance is low and is not preferable. Furthermore, the Sm value is less than 4 nm or more than 300 nm, the long-term stability of the anti-fogging performance is low and is not preferable. It is further preferable that the dents and projections have an arithmetical mean roughness (Ra) from 5 to 30 nm and mean interval (Sm) from 5 to 150 nm therebetween. In this range, the long-term stability of the anti-fogging performance is further preferable. Herein, Ra value and Sm value are defined by a method regulated in Japanese Industrial Standards JIS B 0601 (1994), and they can be calculated on the basis of section curves observed and measured by an atomic force microscope (for example, Seiko Electronic Co., Ltd., Type SPI3700) and an electron microscope (for example, Hitachi, Limited, Type H-600).
Dents and projections on the surface of photocatalytic film can be produced by a method of laminating a thin photocatalytic film on the glass substrate surface so as not to spoil the dents and projections after an alkali shut-off film having dent and projection surface is formed, or a method of directly denting and projecting the photocatalytic film itself.
[Dent and projection alkali shut-off film]
In a case where the surface of titanium oxide based photocatalytic film is dented and projected by forming an alkali shut-off film having a dent and projection surface, the alkali shut-off film can be preferably formed by a sol-gel method or a liquid-phase deposition method.
The dent and projection alkali shut-off film by a sol-gel method is formed by coating a coating liquid containing metal oxide fine particles, and hydrolyzable, condensable and polymerizable organometallic compound or containing chlorosilyl group contained compound or their hydrolyzed substances onto a glass article, drying and as necessary thermally treating the same.
As the abovementioned metal oxide fine particles, a metal oxide fine particles of a monocomponent selected from a group consisting of silicon oxide (silica), aluminium oxide (alumina), zirconium oxide (zirconia), titanium oxide (titania), cerium oxide (ceria), or a complex metal oxide fine particle consisting of metal oxide fine particles, mixtures thereof, and two or more constituents thereof may be used. These are preferably used in a form of solvent diffusion sol (colloid solution). The following are available as a metal oxide sol; for example, xe2x80x9cSnowtex-OLxe2x80x9d, xe2x80x9cSnowtex-Oxe2x80x9d, xe2x80x9cSnowtex-OUPxe2x80x9d, xe2x80x9cSnowtex-UPxe2x80x9d, which are silica sols made by Nissan Chemical Industries, Ltd., xe2x80x9cAlumina sol 520xe2x80x9d which is an alumina sol made by Nissan Chemical Industries, Ltd., xe2x80x9cZirconia sol NZS-30Axe2x80x9d which is a zirconia sol made by Nissan Chemical Industries, Ltd., xe2x80x9cTitania sol CS-Nxe2x80x9d which is a titania sol made by Ishihara Industries CO., Ltd., xe2x80x9cNeedlar U-15xe2x80x9d which is a ceria sol made by Taki Chemical Co., Ltd., etc. All of which are water dispersion sols available on the market, and xe2x80x9cIPA-STxe2x80x9d and xe2x80x9cXBA-STxe2x80x9d made by Nissan Chemical Industries, Ltd, which are an organic solvent dispersion silica sol available on the market may be listed.
It is preferable that the grain size of the abovementioned metal oxide fine particles is from 4 through 300 nm. If the grain size of metal oxide fine particles is less than 4 nm, the arithmetic mean roughness (Ra) is liable to become less than 1.5 nm and the mean interval (Sm) of dents and projections is liable to become less than 4 nm, no effective dent and projection to improve the anti-fogging capacity, anti-fogging sustainability and hydrophilicity sustainability can be formed, and it is not preferable. To the contrary, if the grain size of metal oxide fine particles exceeds 300 nm, the arithmetic mean roughness (Ra) becomes more than 80 nm and the mean interval (Sm) of dents and projections exceeds 300 nm, wherein the dents and projections are too large, resulting in spoiling the transparency, and since the fine particles are liable to be deposited in the process of production, it is not favorable.
Chain fine particles are preferable as the abovementioned metal oxide fine particles. By using chain fine particles, usually colloid chain fine particles, the shape of the surface dents and projections becomes three-dimensionally cubic and convex and concave, wherein it is possible to form surface dents and projections which have a high anti-fogging capacity, anti-fogging sustainability, and hydrophilicity sustainability respective improved. xe2x80x9cSnowtex-OUPxe2x80x9d and xe2x80x9cSnowtex-UPxe2x80x9d which are chain silica sols made by Nissan Chemical Industries, Ltd. may be available as an example of chain colloids. These have a diameter from 10 through 20 nm and a length from 40 through 300 nm.
As a solvent of the abovementioned fine particles, a monocomponent or mixture of water, methanol, ethanol, propanol, etc. is preferable, and water is further preferable.
As hydrolyzable, condensable and polymerizable organometallic compound contained in a coating liquid for forming a dent and projection alkali shut-off film along with the abovementioned metal oxide fine particles, metal alkoxide, for example, methoxide, ethoxide, propoxide, buthoxide, etc. of silicon, aluminium, zirconium, titanium, etc. may be used independently or in combination thereof, and macromolecular type alkyl silicate, for example, xe2x80x9cethylsilicate 40xe2x80x9d made by Colcoat, Ltd., and xe2x80x9cMS56xe2x80x9d made by Mitsubishi Chemical, Ltd. may be also used.
As a hydrolyzed substance of the abovementioned organometallic compound, a alkoxy silane hydrolyzed liquid which is available on the market, for example, xe2x80x9cHAS-10xe2x80x9d made by Colcoat, Ltd., xe2x80x9cCeramica G-91xe2x80x9d and xe2x80x9cG-92-6xe2x80x9d made by Nippan Lab., Ltd., and xe2x80x9cAtron NSI-500xe2x80x9d made by Nippon Soda, Ltd. etc. may be used.
A chlorosilyl group based compound containing in a coating liquid for forming a dent and projection alkali shut-off film along with the abovementioned metal oxide fine particles is a compound having at least one chlorosilyl group (xe2x80x94SiClnX3-n, wherein n is 1, 2, or 3, X is hydrogen, or is alkyl group, alkoxy group, or alcyloxy group respectively having the number of carbon from 1 to 10) in a molecule. Of them, a compound having at least two molecules of chlorine is preferable, wherein chlorosilane or its condensed and polymerized substance, in which at least two hydrogens of silane SinH2n+2 (herein n is an integer from 1 to 5) are substituted by chlorine with the other hydrogens substituted by the abovementioned alkyl group, alkoxy group or acyloxy group as necessary, is preferable. For example, tetrachlorosilane (silicon tetrachloride, SiCl4), trichlorosilane (SiCHl3), trichloromonomethylsilane (SiCH3Cl3), dichlorosilane (SiH2Cl2), and Clxe2x80x94(SiCl2O)nxe2x80x94SiCl3 (wherein n is an integer from 1 to 10) , etc. may be listed.
A hydrolyzed substance of the abovementioned chlorosilyl group contained compound may be used independently or in combination thereof. However, most preferably, chlorosilyl group contained compound is tetrachlorosilane. Chlorosilyl group has a very high reactivity and forms a dense film by self condensation or condensation reaction with a substrate surface.
A solvent of solution containing the abovementioned organometallic compound, chlorosilyl group contained compound or their hydrolyzed substances may be fundamentally any type if the abovementioned organometallic compound or chlorosilyl group contained compound or their hydrolyzed substance is substantially dissolved therein. However, alcohol groups such as methanol, ethanol, propanol, buthanol, etc. are most preferable, and the abovementioned organometallic compound, chlorosilyl group contained compound, or their hydrolyzed substance is contained at a concentration ratio from 1 to 30 percent by weight in total.
Water is requisite to hydrolyze the abovementioned organometallic compounds. This may be either acidic or neutral. However, in order to accelerate the hydrolysis, it is preferable that water which is acidified with hydrochloric acid, nitric acid, sulfuric acid, acetic acid, citric acid, sulfonic acid, etc. is used. The quantity of addition of acid is not specially specified. However, it is better that the quantity thereof is 0.001 through 5 (molar ratio) with respect to the quantity of organometallic compounds. If the quantity of addition thereof is less than 0.001 (molar ratio), the promotion of hydrolysis of organometallic compounds is not sufficient, which is not preferable. And if the addition exceeds 5 (molar ratio), no effect of improving the hydrolysis is increased, which is not preferable.
The quantity of addition of water necessary for the hydrolysis of the abovementioned organometallic compound may be 0.1 through 100 (molar ratio) with respect to the quantity of organometallic compounds. If the water addition quantity is less than 0.1 (molar ratio), the promotion of hydrolysis of organometallic compounds is not sufficient, and if the molar ratio exceeds 100, the solution is liable to be unstable. This is not preferable.
In a case where the abovementioned chlorosilyl group contained compound is used, it is not necessarily a requisite that water or acid is added. Even though no water or acid is additionally added, the hydrolysis is carried out with water contained in the solvent or water in the atmosphere. Furthermore, hydrochloric acid is made free in the solution in line with the hydrolysis, wherein the hydrolysis is further promoted. However, there is no problem if water or acid is additionally supplied.
If the content of the abovementioned fine particles in a film is too small, an effect of adding fine particles, that is, an anti-fogging property and anti-fogging sustainability is not sufficient and not preferable. To the contrary, if the content of fine particles is too large, the matrix phase of metal oxides resulting from organometallic compounds or chlorosilyl group contained compounds is made non-continuous to cause the dents and projections of film to be weakened, wherein the film is liable to be made weak, and further the anti-fogging property and anti-fogging sustainability obtained are saturated to cause no further practical improvement to occur. Therefore, it is preferable that the content of fine particles is 5 or more percent by weight and 80 or less percent by weight when converted to the metal oxides. It is further preferable that the content is 10 or more percent by weight and 70 or less percent by weight and still further preferable that the content thereof is 20 or more percent by weight and 60 or less percent by weight.
The abovementioned metal oxide fine particles are mixed with the abovementioned organometallic compound, chlorosilyl group contained compound or their hydrolyzed substance along with a solvent. As necessary, water, acid catalyst and dispersion assisting agent is added thereto, and a coating liquid to form dents and projections on a substrate is adjusted. At this time, organometallic compound and chlorosilyl group contained compound may be used independently or may be used as a mixture thereof.
The abovementioned organometallic compound or chlorosilyl group contained compound is dissolved in a solvent, to which a catalyst and water are added, and hydrolysis is carried out for five minutes to two days at an appointed degree of temperature from 10xc2x0 C. to the boiling point of the solution, wherein metal oxide fine particles are added to the solution along with a dispersion assisting agent as necessary. In this condition, if necessary, the solution is further hydrolyzed for five minutes to two days at an appointed degree of temperature from 10xc2x0 C. to the boiling point thereof, whereby a coating liquid for forming a dent and projection alkali shut-off film can be obtained. Furthermore, in a case where a chlorosilyl group contained compound is used, it is not necessary that a catalyst and water are added thereto. Still furthermore, metal oxide fine particles may be added before the abovementioned hydrolysis process is started. Furthermore, in order to omit the hydrolysis process of organometallic compounds, a solution in which organometallic compounds are hydrolyzed, which is available on the market, may be used. Thereafter, the obtained coating liquid may be diluted by a suitable solvent in compliance with the coating method.
The grain size, grain profile of metal oxide fine particles in the abovementioned coating liquid, or blending ratio of organometallic compound or chlorosilyl group contained compound or their hydrolyzed substances and metal oxide fine particles, and solid concentration, etc. adjusted so that the surface roughness of the dent and projection alkali shut-off film has an appointed arithmetical mean roughness (Ra) and mean interval (Sm) of dents and projections.
Next, as regards a dent and projection alkali shut-off film by a liquid-phase deposition method, a dent and projection alkali shut-off silicon oxide film is formed, for example, by silicon oxide being deposited onto the surface of a substrate from the abovementioned water solution by immersing a silicate glass substrate in a silica supersaturation solution of silicofluoride hydroxide having a concentration from 1 to 4 mol/L for 1 to 4 hours at a temperature of 25xc2x0 C. to 50xc2x0 C., and simultaneously by silica fine particles dispersed and existing in the abovementioned water solution being adhered to the surface of the substrate. Water solution of the abovementioned silica supersaturation silicofluoride hydroxide can be obtained by being dissolved in a silicofluoride hydroxide water solution having a concentration from 1 to 4 mol/L and further adding boric acid thereto so that its concentration is 1xc3x9710xe2x88x924 to 100xc3x9710xe2x88x924 mol/L.
[Denting and projecting photocatalytic films themselves]
As a method for forming dents and projections on a surface by directly denting and projecting titanium oxide based photocatalytic films themselves without denting and projecting the surface of alkali shut-off film,
(a) method of etching by using plasma and fluoric acid, etc. after a titanium oxide based photocatalytic film is formed,
(b) for example, in a case where a titanium oxide based photocatalytic film is formed by a sol-gel method, a method for adding organic macromolecules or macromolecular fine particles of polyethylene glycol, polystyrene, etc. to or dispersing the same into a coating liquid,
(c) for example, in a case where a titanium oxide based photocatalytic film is formed by a sol-gel method, a method for preferably adding and dispersing colloid-like metal oxide fine particles (for example, titanium oxide fine particles, silicon oxide fine particles, aluminium oxide fine particles, zirconium oxide fine particles, cerium oxide fine particles) into a coating liquid main composed of titanium alkoxide,
(d) for example, in a case where a titanium oxide based photocatalytic film is formed by a sol-gel method, a method for preferably adding and dispersing colloid-like metal oxide fine particles containing at least titanium oxide fine particles into a coating liquid main composed of metalix alkoxide (for example, silicon alkoxide, zirconium alkoxide, aluminium alkoxide) other than titanium, and
(e) for example, in a case where a titanium oxide film is formed by a sol-gel method, a method for producing a large grains by condensing and polymerizing titanium alkoxide by adding alkali, increasing the amount of water addition, or reducing a stabilizer agent, etc. when producing a coating liquid containing titanium alkoxide or its hydrolyzed substance may be listed.
Of these methods, method (a) is not preferable because the number of processes is increased, and method (d) is not preferable since there is a case where the film quality of titanium oxide film is lowered to cause the mechanical strength to be lowered, the transparency to be spoiled, and the photocatalytic activity to be lowered. Methods (b), (c) and (d) are preferably used, by which a dent and projection titanium oxide film can be comparatively easily obtained. It is preferable that the size of fine particles used in the abovementioned methods (b), (c) and (d) is from 4 to 300 nm by the similar reason in a case of the abovementioned dent and projection alkali shut-off film. Furthermore, the abovementioned chain fine particles are preferable as metal oxide fine particles.
According to the abovementioned method (d), 1) a dent and projection thin film where titanium oxide fine particles are dispersed in the matrix composed of metal oxide fine particles other than titanium oxide, and 2) a dent and projection thin film where titanium oxide fine particles and other metal oxide fine particles are dispersed in the matrix composed of metal oxide fine particles other than titanium oxide, can be respectively obtained.
[Layer for preventing organic substances from being adhered]
It is preferable that a layer for preventing organic substances from being adhered as described below is formed on the abovementioned photocatalytic dent and projection film.
A photocatalytic film such as a titanium oxide film having a high activity has a small contact angle which is 5 degrees or less, just after being irradiated by ultraviolet rays, and has a considerably good anti-fogging property at initial stage. However, since organic substances are easily adhered to the surface thereof, the anti-fogging property may be deteriorated chronologically due to an increase of adsorbed organic substances. In the invention, it is preferable that a SiOx monocomponent equivalent layer (x is 1 or 2) is formed, whereby adsorption of organic substances can be effectively suppressed while maintaining a high photocatalytic activity, and the anti-fogging property can be prevented from being deteriorated.
An SiOx monocomponent equivalent layer, which is a layer for preventing organic substances from being adhered, can be preferably formed through decomposition by being irradiating with ultraviolet light or being heated under a presence of oxygen after steam of silicon oxide compounds such as 1,3,5,7-tetramethylcychlotetrasiloxane is chemically adsorbed onto the surface of the photocatalytic film, and organic silicon oxide compounds, for example, liquid containing tetraalkoxysilane is coated onto the surface of the photocatalytic film. In addition thereto, an SiOx monocomponent equivalent layer may be directly formed by a vacuum deposition method, an LB method, or a liquid-phase deposition method, etc. Instead of SiOx monocomponent equivalent layer, a stain preventing property can be remarkably increased by covering the photocatalytic film surface with an organometallic compound or its hydrolyzed substance containing in molecule at least a function group selected from a group consisting of polyalkylene oxide group, alkyl group, alkenyl group and aryl group. These organometallic compound is gradually decomposed by external factors such as irradiation of ultraviolet light and temperature rise and finally forms a metal oxide monocomponent equivalent layer such as SiOx, etc., and the stain preventing property can be maintained. Here, a monocomponent equivalent layer is substantially a monocomponent layer which indicates a layer of molecules in which 0.5 to 5 molecules are disposed in average in the direction of thickness.
Polyethylene oxide group, polypropyrene oxide group, etc. may be mainly used as polyalkylene oxide group contained in molecules of the abovementioned organometallic compound. As the abovementioned alkyl group, a chain alkyl group having a carbon atom number from 1 to 10 such as methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, octyl group, nonyl group, decyl group, etc., and ring alkyl group having a carbon atom number from 3 to 10 such as cyclopentyl group, cyclohexyl group, etc. may be mainly used. As the abovementioned alkenyl group, a group having a carbon atom number from 1 to 10 such as vinyl group, allyl group, butenyl group, propenyl group, hexenyl group, octenyl group, cyclohexenyl group, etc. is mainly used. Phenyl group, tolyl group, xylyl group, etc. may be mainly used as the abovementioned aryl group.
As these functional groups, for example, organometallic compound containing polyethylene oxide group in molecules, organosilane such as [alkoxy(polyethyleneoxy)alkyl]trialkoxysilane, [alkoxy(polyethyleneoxy)alkyl]trichloro-silane, and a organic titanium compound such as [alkoxy(polyethyleneoxy)alkyl]trialkoxy titanium may be listed.
Since these functional groups are nonpolar or has low polarity, stains are less adhered to cause an increase of the contact angle to be suppressed with respect to water drops, that is, it is preferable since the anti-fogging sustainability and hydrophilicity sustainability is improved. In particular, as regards the abovementioned anti-fogging and stain-prevented articles which are produced by using organosilane including polyalkylene oxide group, the anti-fogging property is excellent, the anti-fogging sustainability and hydrophilicity sustainability (that is, stain preventing property) is specially excellent, and especially, as described above, if the hydrophilicity sustainability is high, the stain preventing property is good.
Since the abovementioned functional group is non-reactive or has low reaction property, no chemical combination with stains is produced to cause stains not to be fixed on the surface. Therefore, since stains adhered onto the surface can be simply eliminated by wiping, etc., the anti-fogging property can be simply revived even though the anti-fogging property goes away due to stains.
It is preferable that organosilane containing the abovementioned polyalkylene oxide group is alkoxysialne and chlorosilane having an alkoxyl group and chloro group in molecules. Since alkoxyl group and chloro group are easily hydrolyzed to cause organosilane to be toughly chemically bonded to the dent and projection surface of photocatalytic film, products having a higher anti-fogging sustainability can be obtained. Of the abovementioned organosilane, alkoxysilane having a polyethylene oxide group, especially, [alkoxy (polyethyleneoxy) alkyl]trialkoxysilane, for example, [methoxy (polyethyleneoxy)propyl]trimethoxysilane is most preferable.
As a method for bonding or adhering the abovementioned organosilane or its hydrolyzed substance to the dent and projection surface of the abovementioned photocatalytic film, any method by which the abovementioned organosilane or its hydrolyzed substance comes into contact with the abovementioned dent and projection surface may be available. For example, a method for coating a liquid containing the abovementioned organosilane or its hydrolyzed substance onto the dent and projection surface (that is, coating method), a method for immersing a photocatalytic dent and projection film formed substance into a liquid containing the abovementioned organosilane or its hydrolyzed substance (that is, a liquid phase chemical adsorption method), a method for placing a photocatalytic dent and projection film formed substance in steam of the abovementioned organosilane or its hydrolyzed substance and adsorbing the same there on (that is, gas phase chemical adsorption method) may be listed.
Of the abovementioned methods, the abovementioned coating method is specially preferable since it is simplest and low in production cost. The abovementioned coating method may use an already known technique, and it is not specially limited. There are many methods which are a method of using a device such as a spin coater, roll coater, spray coater, curtain coater, etc., an immersing method (dip coating method), a flow-coating method, a method for rubbing the photocatalytic dent and projection film surface with a cloth or paper impregnated with a coating liquid in a state where the cloth or paper is brought into contact with the surface (rubbing method), and various kinds of printing methods such as a screen printing, gravure printing, curved printing, etc.
A solvent for dissolving the abovementioned organosilane is not specially limited. However, preferably, water, alcohol, ketone, etc. may be employed along or by combination thereof in view of safety, cost, and operation efficiency. Methanol, ethanol, propanol, butanol, etc. may be listed as alcohol, etc. Acetone, methylethyl ketone, diethyl ketone, etc. may be employed as ketone, etc.
The abovementioned organosilane may be hydrolyzed for use as necessary. Water and acid catalyst may be added to organosilane solution as necessary, wherein hydrolysis is carried out for a fixed period of time at a fixed temperature, and organosilane is diluted for use as necessary.
Although the conditions of hydrolysis of organosilane are not specially limited, it is preferable that the hydrolysis is carried out for three minutes to fifty hours in an range of temperature from 20xc2x0 C. to 60xc2x0 C. In a case where the temperature is lower than 20xc2x0 C. or the time is less than 3 minutes, the promotion of hydrolysis is not sufficient. To the contrary, if the temperature is higher than 60xc2x0 C. and the time exceeds 50 hours, the effect of promotion of hydrolysis can not be enhanced, the service life of the coating liquid is shortened. Therefore, that is not preferable.
As the abovementioned acid catalyst, mineral acids such as hydrochloric acid, sulfuric acid, nitric acid, etc., and organic acids such as acetic acid, formate acid, citric acid, para-toluenesulfonic acid, etc. may be used. The quantity of addition of acid is not specially limited. However, it is good that the quantity of addition of acid is from 0.0001 to 5 (molar ratio) with respect to organosilane. If the quantity of addition of acid is less than 0.0001 (molar ratio), promotion of hydrolysis of organosilane is not sufficient, and if the same exceeds 5 (molar ratio), the effect of hydrolysis promotion is no more improved. The acid becomes excessive to be unfavorable.
Though the quantity of water added for the abovementioned hydrolysis is not specially limited, it is good that the quantity is 0.1 or more (molar ratio) with respect to organosilane. If the quantity is less than 0.1 (molar ratio), promotion of the hydrolysis of organosilane is not sufficient to be unfavorable.
On the other hand, as regards polyalkylene oxide group contained organosilane having a great hydrolysis speed like, for example, [alkoxy(polyethyleneoxy)alkyl]trichlorosilane, there may be a case where the hydrolysis can be promoted with only water adsorbed by the dent and projection film surface of light catalyst, and it is fixed on the surface by a dehydration/condensation reaction. In this case, since an anti-fogging article which is superior in view of weathertightness, anti-fogging and stain preventing property, anti-fogging sustainability and hydrophilicity sustainability, can be obtained, it is preferable that a coating liquid is prepared by using an nonacqueous solvent with the dissolved water sufficiently decreased. As an nonacqueous solvent, n-hexane, cyclohexane, xylene, toluene, etc. may be listed.
Furthermore, the concentration of organosilane solution used for coating is not specially limited, organosilane of 0.001 through 5 percent by weight is preferably used. If the concentration is lower than 0.001 percent by weight, no sufficient promotion of anti-fogging sustainability and hydrophilicity sustainability of an anti-fogging and stain-prevented article obtained can be recognized, and if the concentration exceeds 5 percent by weight, the anti-fogging property and stain preventing property are not improved anymore. Therefore, that is not economical and is not preferable.
It is preferable that the dent and projection film of photocatalyst on which organosilane solution is coated is dried or heat-treated at a temperature from 20 through 180xc2x0 C. for three minutes to three hours. By this treatment, bonding of organosilane onto the dent and projection film surface of photocatalyst is strengthened to cause the durability, anti-fogging sustainability and hydrophilicity sustainability of an anti-fogging and stain-prevented article to be improved. If the temperature is less than 20xc2x0 C. or the treatment time is shorter than three minutes, the abovementioned effect is not sufficient to be unfavorable. Since there is a case where organosilane is decomposed if the temperature is higher than 180xc2x0 C. That is also unfavorable. Furthermore, even though the treatment time exceeds three hours, no more effect can be expected. Therefore, that is also unfavorable in view of the productivity.
If organosilane forms a monocomponent equivalent layer on the abovementioned dent and projection film surface of the photocatalyst, the anti-fogging sustainability and stain preventing property can be improved. The organosilane layer is gradually decomposed by external factors such as irradiation of ultraviolet rays, temperature rises, etc., and finally becomes a monocomponent equivalent layer of SiOx, wherein the anti-fogging sustainability and stain preventing property are maintained. Even in a case where the thickness of organosilane layer is comparatively large, it is necessary that the thickness of organosilane layer is not greatly fluctuated on places, and it is preferable that dents and projections which are similar to those of the abovementioned dent and projection film of photocatalyst surface, that is, dents and projections having an arithmetical mean roughness (Ra) from 1.5 to 80 nm and an average interval (Sm) of the dents and projections from 4 to 300 nm, are formed on the outside surface of the organosilane layer. Furthermore, preferable dents and projections are such that their arithmetical mean roughness (Ra) is 5 to 30 nm and the mean interval (Sm) of dents and projections is 5 to 150 nm.
The above describes a case of an anti-fogging and stain-prevented article having dents and projections, which have an arithmetical mean roughness (Ra) from 1.5 to 80 nm and a mean interval (Sm) from 4 to 300 nm, formed on the surface of titanium oxide based photocatalytic film. However, instead of such a titanium oxide based photocatalytic dent and projection film, by covering an organic substance adhesion preventing layer made of a silicon oxide layer or a layer of organosilane or its hydrolyzed substance containing at least one functional group selected from a group consisting of polyalkylene oxide group, alkyl group, alkenyl group and aryl group, on a titanium oxide based photocatalytic film not having any surface dent and projection, it is possible for organic substances to be prevented from being adhered onto the titanium oxide based photocatalytic film surface, and it is possible to suppress a deterioration of hydrophilicity due to an increase of adsorbed organic substances, whereby an excellent stain preventing property can be maintained. The description of this organic substance adhesion preventing layer is omitted because the abovementioned organic substance adhesion preventing layer employed for titanium oxide based photocatalytic dent and projection film can be used as it is.